调用canvas.drawText（）时发生NullPointerException。为什么？

Question

这是我之前询问的问题的后续内容。基本上我有一个游戏，主要动作发生在一个自View类扩展的自定义类的画布上。

我将分数保存在一个字符串中，我试图将它绘制到屏幕的左上角。

在我的onDraw（）方法的底部，我有下面的代码行：

canvas.drawText(score, 5, 5, null); 

当我试图运行游戏，登录猫给了我以下错误：

03-02 22:30:29.955: ERROR/AndroidRuntime(8140): FATAL EXCEPTION: main 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140): java.lang.NullPointerException 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.graphics.Canvas.drawText(Native Method) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at com.mattdrewery.supercatch.GameView.onDraw(GameView.java:143) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.view.View.draw(View.java:6880) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.view.ViewGroup.drawChild(ViewGroup.java:1646) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.view.View.draw(View.java:6883) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.widget.FrameLayout.draw(FrameLayout.java:357) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.view.ViewGroup.drawChild(ViewGroup.java:1646) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.view.ViewGroup.drawChild(ViewGroup.java:1644) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.view.View.draw(View.java:6883) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.widget.FrameLayout.draw(FrameLayout.java:357) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1862) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.view.ViewRoot.draw(ViewRoot.java:1522) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.view.ViewRoot.performTraversals(ViewRoot.java:1258) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.view.ViewRoot.handleMessage(ViewRoot.java:1859) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.os.Handler.dispatchMessage(Handler.java:99) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.os.Looper.loop(Looper.java:123) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at android.app.ActivityThread.main(ActivityThread.java:3683) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at java.lang.reflect.Method.invokeNative(Native Method) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at java.lang.reflect.Method.invoke(Method.java:507) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
03-02 22:30:29.955: ERROR/AndroidRuntime(8140):  at dalvik.system.NativeStart.main(Native Method) 

Answer 1

您的Paint参数不能为空。

初始化它的某处（不在onDraw）;

Paint mPaint = new Paint(); 

canvas.drawText(score, 5, 5, mPaint);